This invention relates generally to devices for removing tree stumps, and, more particularly, to tractor-mounted stump grinders, e.g., stump grinder attachments capable of being mounted on a three-point hitch of a tractor.
A number of different techniques are known for removal of tree stumps, including the use of explosives, mechanical force such as by a bulldozer, and also by comminuting or grinding the stump down to ground level and preferably below. Stump grinding has advantages over other techniques for stump removal, such as greater safety than the use of dynamite, less damage to lawns or ground surfaces surrounding the stump than with the use of bulldozers or other heavy equipment.
Numerous types of equipment for grinding stumps have been devised over the years. For example, it is known to mount stump cutter teeth on one or both faces of a cutter disc or wheel which is mounted transversely, i.e., across the longitudinal axis of a machine support frame or swing arm, with the machine moving the cutter wheel forward or backward along that axis against a portion of a stump, whereby the teeth on one face contact and grind that portion. It is also known to mount stump cutter teeth on one or both faces of a cutter wheel which is swung from side to side during a cutting operation with the teeth on one face or the other contacting and grinding a stump from the side. Examples of this latter type of equipment are described in the following patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,601,366 Chapman Jun. 24, 1952 2,887,134 Bartlett May 19, 1959 2,927,613 Franzen Mar. 8, 1960 3,198,224 Hiley Aug. 3, 1965 3,732,905 Pickel May 15, 1973 3,911,979 Rousseau Oct. 14, 1975 4,681,145 York Jul. 21, 1987 4,709,736 Bellars Dec. 1, 1987 ______________________________________
Especially for tractor-mounted stump grinders, it is conventional to restrict the motion of the cutter wheel assembly to one degree of freedom and to rely on the mobility of the vehicle to which the stump grinder is attached, e.g., a tractor, for additional adjustments of position of the cutter wheel which may be necessary during operation, particularly for large tree stumps. For example, the stump grinders disclosed in the above-referenced patents to Chapman and Pickel are mounted on a hydraulically actuated tractor hitch and affixed thereto such that side to side cutting action relative to the longitudinal axis of the tractor is possible but longitudinal motion of the cutting assembly relative to the tractor is impossible.
It is time-consuming and otherwise inconvenient to move a tractor during a cutting operation, particularly the type of tractor having a power take-off (PTO) which is used to drive the cutter wheel, as in Pickel. A PTO-driven stump grinder is a substantial load on a tractor's engine and, therefore, as a practical matter must be disengaged before the tractor is driven. Repositioning of the tractor requires not only shifting of gears, but also allowance of time for the cutter wheel to substantially stop spinning and thereby avoid damage or excessive wear on the tractor drive train and the stump grinder that could otherwise result from the high inertia of the cutter wheel upon re-engagement of the PTO after moving the tractor.
The repositioning problem has been recognized and different solutions proposed. U.S. Pat. No. 2,927,613 to Franzen et al. discloses a cutting head mounted on an auxiliary frame which is arranged to slide longitudinally along a mainframe which in turn is pivotally mounted on a tractor drawbar for vertical and horizontal pivotal movement with respect thereto. There is no indication in the Franzen et al. patent that it would be useful to mount a stump grinder on a hydraulically actuated hitch, either for initial positioning or cutting height adjustment, for example, or for somehow facilitating greater stabilization for the stump grinder during use than would normally be possible with a drawbar fixed-mounted to a tractor frame.
U.S. Pat. No. 3,198,224 to Hiley proposes a stump grinder mounted on the end of a foldable boom which is attached directly to the rear frame of a tractor by means of a pivot mechanism fixed-mounted to the tractor frame. Hiley proposes the use of tractor-mounted legs which are lowered and firmly set on the ground after the tractor is moved into position near a stump. Such a stump grinder is not suitable for use on a conventional, general purpose tractor.
The problem of repositioning a tractor was also recognized in the mid-1980s by Bellars, as disclosed in U.S. Pat. No. 4,709,736, in the context of moving the tractor from stump to stump. Sellers proposes an overrun device including a one-way valve and a shutoff valve to allow the cutter wheel to continue rotating when the tractor engine is slowed down. Bellars also suggests that a three-point hitch provides inadequate stability for a stump grinder, and for additional stabilization suggests an auxiliary mounting member anchored to the tractor by left and right side brackets bolted securely to the rear axle of the tractor. Such a construction unnecessarily adds to the complexity of the stump grinder and makes it more difficult and time-consuming to attach the stump grinder to the tractor for use.
In spite of decades of activity in this area there remains a need for a relatively low-cost, reliable, easily operated, stable stump grinder capable of providing smooth yet relatively rapid cutting action.